Chronic premature ventricular extrasystoles are an ominous premonitory sign of serious and often fatal cardiac arrhythmias. Theoretically, control of the extrasystoles should decrease the incidence of sudden death due to coronary artery disease. The currently available oral antiarrhythmic agents require frequent administration, are often ineffective, and possess a low toxic-therapeutic dose ration. Xylocaine, a potent antiarrhythmic of low toxicity, if administered parenterally on a chronic basis utilizing an easily implantable permanent infusion device should offer protection to patients at risk. By implanting the infusion pump in mongrel dogs and evaluating them periodically, it is proposed that: (1) The efficacy of the infusion pump be evaluated for maintaining therapeutic xylocaine blood levels over prolonged period, (2) The long-term xylocaine toxicity be determined.